Abstract

MINI: Study evaluates the efficacy of CyberKnife® (CK) SRS for thyroid spinal metastases (SM). Patients with SMs from thyroid carcinoma that were treated with CK SRS between 2003 and 2013were identified. CK can be safely used to treat SMs from thyroid cancer with a high rate of local control. STUDY DESIGN A retrospective data review. OBJECTIVE To evaluate the efficacy of CyberKnife® SRS for thyroid SMs. SUMMARY OF BACKGROUND DATA Thyroid carcinoma is an infrequent cause of spinal metastasis (SM). The absolute efficacy of stereotactic radiosurgery (SRS) generally and CyberKnife® (CK) in particular remains poorly characterized for thyroid SM. The current study is the first to specifically evaluate the efficacy of CyberKnife® SRS for thyroid SMs. METHODS A retrospective review of patients at our institution between 2003 and 2013 was done. Details about tumor location, radiographic findings before and after CK SRS, tumor recurrence, prescription isodose level, total and maximum dose, number of fractions, and gross tumor volume coverage were similarly collected. For comparison with other studies, the biologically effective dose (BED) and the equivalent total dose in 2Gy fractions (EQD2) were calculated. Each patient was assessed for survival and local disease control from the time of the first CK session and survival analysis was carried out using the Kaplan-Meier method. Risk factors for local failure were assessed using multivariate logistic regression. RESULTS A total of 12 patients with 32 spinal metastases from thyroid carcinoma that were treated with CK SRS were identified. Survival for 1, 2, and 3 years was 55%, 44%, and 33%, and local control was 67%, 56%, and 34% respectively. The study found that the single strongest factor associated with local control was prior radiotherapy (β-coefficient -27.72, p = 0.01). No complications occurred in the immediate or late follow-up period. CONCLUSION This was the first study to specifically investigate the efficacy of CK for treatment of thyroid SMs. Our findings suggest that CK can be safely used to treat spinal SMs from thyroid cancer and is associated with a high rate of local control. LEVEL OF EVIDENCE 4.